The present invention generally relates to welding and particularly to scissor-type resistance butt welding machines.
Known in the art is a device for controlling the operation of a rail welding machine. The device includes hydraulic cylinders for clamping two welded rails in two pairs of machine jaws each mounted on one of two machine's pillars, a transfer hydraulic drive, a hydraulic fluid supply system and a control system ("Equipment for Resistance Welding of Rails and its Operation" edited by Kuchuk-Yatsenko S. I., Kiev, 1974, p. 52). When one of the machine pillars includes flash trimming cutters emcompassing a rail along its entire perimeter (USSR Application No. 2027967/25-27, July 26, 1974), the prior art circuit controlling the release of the jaws and machine transfer does not provide for the possibility of selectively releasing a rail web by one pair of jaws mounted on the same pillar on which the cutters are mounted while keeping the other pair of jaws clamped, and does not allow the subsequent accelerated advance of the machine pillar with the cutters mounted thereon to remove the flash at the welded joint.
Also known in the art is a device for controlling the operation of a plier or scissor-type rail welding machine that is employed for welding rails together in situ. See, for example, U.S. Pat. No. 3,349,216. Such devices typically include two clamping hydraulic cylinders for clamping the welded rails in machine clamping jaws, each cylinder being associated with a pair of plier-type clamps interconnected by a common shaft and by the rods of two upset hydraulic cylinders, a hydraulic fluid supply system, an electrohydraulic transfer drive which includes a follow-up hydraulic slide valve and a reversible hydraulic slide valve controlling the clamping and unclamping of both welded rails only, however, simultaneously. Flash is sheared off the rails joined together on the machine by means of air chisels after the rails have been taken out of the welder and the latter has been carried aside. According to another embodiment, flash trimming is effected in special purpose gears disposed externally of the welding machine. As the welded rails are taken out of the welder and set up in the flash trimming gear, the joint cools off and the flash trimming operation thereby requires a considerable force to be applied.
A need for simultaneous clamping or releasing of both pairs of the plier-type clamps is dictated by the designs of the described prior art welding machines of the scissor-type which provide for alignment of the welded parts during welding. However, the machine design allows relieving one of the welded parts of the clamping force without appreciable release of the plier-type clamps.
In butt welding machines of the non-plier type adapted for operation under stationary conditions, each clamping cylinder is controlled individually with the aid of an individual hydraulic slide valve. Therefore, flash trimming in said machines can be effected without introducing any changes in the machine design by making use of the available machine control device.
The release of the jaws, mounted on the same movable pillar on which the cutters are mounted, is adjusted either by means of limit switches or visually.
However, on these machines accurate alignment of welded parts, rails in particular, poses a serious problem.
The plier welding machines are more mobile, enabling the rails or the entire lengths to be welded both under stationary and field conditions, directly in track, and ensuring automatic alignment of the welded rails.
To relieve the clamping force by any pair of clamping jaws it has been found to be sufficient to interconnect the rod space and the piston space of a corresponding clamping cylinder. In this case, the same pressure will be established in both spaces, the piston being carried upwards together with its rod, owing to a difference in its effective areas, and thereby separating the corresponding plier-type clamps. Both said spaces of the clamping cylinder can be connected simultaneously either to the drain or delivery manifold. In the first case a negligible pressure will be developed in said spaces and the piston with the clamping cylinder will be displaced a small distance releasing the clamping jaws without appreciable unclamping of said plier-type clamps, and the flash trimming cutters will be brought into a position minimizing the amount of the flash remaining upon its cutting off.
Where both said spaces of the clamping cylinder are connected to the delivery manifold, a rather great pressure will be established in said spaces, this resulting not only in relieving the clamping force but in appreciable releasing of said plier-type clamps. To preclude this it is necessary to mount a reduction valve, adjusted for a certain low operating pressure in each manifold connected to said clamping cylinder spaces which will make the design of said device more sophisticated and affect reliability thereof.
A device for removing flash after resistance butt welding of rails is described in U.S. Pat. No. 3,978,746. This patent discloses a plier or scissor-type rail welding machine which includes two spaced cases or pillars which are coupled to each other and made movable relative to each other by hydraulic cylinder arrangements. The patent discloses an arrangement of cutters mounted on one of the pillars or cases, which cutters are adapted to embrace the rail rolling surface, as well as the sides of the rail head, the web and the base flange of the rail. Initially, the rails are pinched or clamped inside each of the two spaced cases or pillars by a hydraulic cylinder. Once the welding process has been completed, one of the cases on which the cutters are mounted is moved by suitable hydraulic cylinders towards the welded joint to remove flash from it. Before the case or pillar with the cutters mounted thereon is set in motion, the clamped rail therein is partly released, but only enough to permit sliding of the rail, and only then is the flash removal operation started. This patent teaches the essential elements of a plier or scissor-type butt welding machine and describes the basic operation thereof. The present invention may be used in conjunction with a butt welding machine of the type disclosed in this patent to make the operation thereof more convenient and reliable.